Cable-driven robots using actuation cables which are generally pulled directly by means of motor-driven pulleys, are known in the prior art. Examples of such prior art actuators are described in the following published articles: “Development of an ultrahigh speed robot FALCON using wire drive system,” by S. Kawamura et al., published in IEEE International Conference on Robotics and Automation, Vol. 1, pp. 215-220, 1995; “Kinematic analysis and design of planar parallel mechanisms actuated with cables,” by G. Barrette et al., published in ASME 26th Biennial Mechanisms and Robotics Conference, Baltimore, USA, No. MECH-14091, 2000; “Workspace and design analysis of cable-suspended planar parallel robots,” by A. Fattah et al., published in Proceedings of the ASME Design Engineering Technical Conference, Vol. 5B, pp. 1095-1103, 2002; Maeda, K., “On design of a redundant wire-driven parallel robot WARP manipulator,” by K. Maeda et al., published in IEEE International Conference on Robotics and Automation, Vol. 2, pp. 895-900, 1999; “Development of a large parallel-cable manipulator for the feed-supporting system of a next-generation large radio telescope,” by Y. X. Su et al., published in Journal of Robotic Systems, Vol. 18, No. 11, pp. 633-643, 2001; “Tension Distribution in Tendon-Based Stewart Platforms,” by R. Verhoeven, et al., published in Advances in Robot Kinematics, edited by J. Lenarcic and F. Thomas, Kluwer Academic Publisher, Spain, 2002; “Translational Planar Cable-Direct-Driven Robot,” by R. L. Williams et al., published in Journal of Intelligent and Robotic Systems, Vol. 37, pp. 69-96, 2003; and “Concept Paper: Cable Driven Robots for use in Hazardous Environments” by A. T. Reichel et al., published by the School of Mechanical Engineering of the Georgia Institute of Technology.
Actuator systems having up to six degrees of freedom using such pulley wound cables have been described in the following published articles: “On the Inverse Kinematics, Statics, and Fault Tolerance of Cable-Suspended Robots” by R. G. Roberts, et al., published in Journal of Robotic Systems, Vol. 15, No. 10, pp. 581-597, 1998; “A Robotic Crane System utilizing the Stewart Platform Configuration” by R. Bostelman, et al., published in International Symposium on Robotics and Manufacturing, Santa Fe, N.Mex., 1992; and “CAT4 (cable actuated truss-4 degrees of freedom): A novel 4 DOF cable actuated parallel manipulator,” by C. Kossowski, et al., published in Journal of Robotic Systems, Vol. 19, No. 12, pp. 605-615, 2002.
Such wire driven robotic actuators are available commercially from companies such as provide SKYCAM surveillance systems, and are characterized by the low inertia and the resulting high acceleration and speed of the robot. Since the main advantages of this structure are its high speed, low inertia and large workspace, the issue of accuracy, which is generally low, has rarely been seriously addressed in prior art cable-driven robot structures. Moreover, the actual pose (position and orientation) of the output in prior art cable-driven robots depends on the wire connecting points at the actuating base, and these points inherently move as the wire is rolled onto the driven pulley or reel, whether the wire builds up layer on top of layer, or whether it moves sideways as it lays down on the pulley side by side. Compensation for this motion of the actuating point is essential if high positional accuracy is required. Mechanical devices used to overcome this problem, such as idler pulleys, guide holes or guide grooves, which define a fixed point of motion origin, add to system friction, inertia and stick-slip effects, thereby further degrading the system accuracy and other characteristics.
There therefore exists a need for a low inertia, high speed cable-type of actuator, which overcomes at least some of the disadvantages of the prior art cable driven actuators.
The disclosures of all publications mentioned in this section and in the other sections of the specification, are hereby incorporated by reference, each in their entirety.